1. Field of the Invention
The present invention relates to a plasma accelerating apparatus, and more particularly, to a plasma accelerating apparatus and a plasma processing system having the same, which is used for semiconductor substrate processing for etching and removing a thin film from a substrate or depositing the thin film on the substrate.
2. Description of the Related Art
In recent years, with the increased need of high speed microprocessors and high recording density memories, a technique of reducing a thickness of a gate dielectric substance and a lateral size of a logic element has been actively developed so that many elements can be mounted on one semiconductor chip. There is a technique of reducing a gate length of a transistor to less than 35 nm, a thickness of a gate oxide to less than 0.5 nm, or increasing a number of metallization levels beyond six as an example of the aforementioned technique.
However, in order to implement such a technique, high performance deposition and/or etching devices capable of increasing a mounting density of a device at the time of manufacturing the semiconductor chip, have been required. Among the high performance deposition and/or etching devices, a plasma etcher or a plasma sputtering system using a plasma accelerating apparatus has been widely used.
FIG. 1 is a schematic cut-away perspective view showing a Hall effect plasma accelerating apparatus 10 used for a plasma etcher or a plasma sputtering system as an example of a conventional plasma accelerating apparatus. The Hall effect plasma accelerating apparatus 10 is disclosed in U.S. Pat. No. 5,847,593.
With reference to FIG. 1, the Hall effect plasma accelerating apparatus 10 includes a circular channel 22 having an upper shielded end and a lower open end. (Note that the lower open end faces up in the figure.) An internal circle coil 16, and external circle coils 17, 18, 18′, and 19 are coaxially positioned at an inside and an outside of the circle channel 22 in a line. The circle coils 16, 17, 18, 18′, and 19 have physically and magnetically isolated polarity to form a magnetic field. A circular anode electrode 24 is connected to a gas supply pipe 25 and ionizes a supplied gas. A cathode electrode 27 is positioned on a magnetic pole of a lower end of a channel 22 and connected to the gas supply line 29, and supplies electrons.
The external circle coils 17, 18, 18′, and 19 are divided into an upper coil 17 and lower coils 18, 18′ and 19 of separated sections. Encircling an outside of the channel 22 is the upper coil 17 and encircling an opening of the channel 22 are the lower coils 18, 18′ and 19. Upper portions of the upper coil 17 and the internal coil 16 are isolated by a dielectric layer 23. A magnetic field of the isolated region is shielded, so that a partially magnetic field intersecting a space portion 20 of the channel 22 is induced at only a region of an opening 22a of the channel 22, but not at an entire portion of the channel 22. A magnetic field formed at positions of the lower coils 18, 18′ and 19 partially captures electrons.
Consequently, the Hall effect plasma accelerating apparatus 10 may accelerate only positive ions, and thus cannot accelerate an electrically neutral plasma by a magnetic field formed due to the presence of the anode electrode 24 and the cathode electrode 27. Furthermore, the Hall effect plasma accelerating apparatus 10 laminates a charge on a surface of a substrate on which ions are deposited, causing a loss such as a charge shunt and nothing to occur in a minute pattern that may lead to a formation of a non-uniform etching profile.
FIG. 2 is a cross-sectional view showing a coaxial plasma accelerating apparatus 40 used for a plasma sputtering system or a plasma etcher as another example of a conventional plasma accelerating apparatus. The coaxial plasma accelerating apparatus 40 is disclosed in an article by J. T. Scheuer, et. al., IEEE Tran. on Plasma Sci., VOL. 22, No. 6, 1015, 1994.
Referring to FIG. 2, the coaxial plasma accelerating apparatus 40 includes a circular channel 50 having an upper shield end and a lower open end. The circular channel 50 accelerates plasma produced by discharging an internally introduced gas. A cylindrical cathode electrode 54 is positioned inside the channel 50. A cylindrical anode electrode 52 is positioned at an outside of an opening of the channel 50, which is coaxially spaced apart from the cylindrical cathode electrode 54 by a predetermined distance. In addition, the coaxial plasma accelerating apparatus 40 includes a control coil 64, a cathode coil 56, and an anode coil 58. The control coil 64 controls plasma in the channel 50. The cathode coil 56 is provided inside the cathode electrode 54. The anode coil 58 is provided outside the anode electrode 52.
The coaxial plasma accelerating apparatus 40 generates an electric current flowing through the channel 50 therein and induces a radial magnetic field enclosing the cathode electrode 54 by the generated current by including a channel 50 and a control coil 64. Here, the channel 50 has inner and outer walls in which the anode electrode 52 and the cathode electrode 54 are provided, respectively, and the control coil 64 is provided at an outside of the channel 50. In the coaxial plasma accelerating apparatus 40, a speed of a plasma ion at an outlet port is very high, for example, of about 500 eV, and a direct current discharge by an anode electrode and a cathode electrode is used, and thus plasma ions accelerated from the anode electrode 52 to the cathode electrode 54 collide with the cathode electrode 54 in the channel 50. The cathode electrode 54 is significantly damaged through the collisions to become difficult to be used for an etching process of a semiconductor thin film deposition process.
In order address these and other problems, an inductively coupled discharge type plasma accelerating apparatus 60 shown in FIG. 3 has been suggested. With reference to FIG. 3, the inductively coupled discharge type plasma accelerating apparatus 60 includes a plasma channel 77, an upper circle loop inductor 79, an internal circle loop inductor 71, and an external circle loop inductor 73.
A gas is ionized and accelerated in the plasma channel 77. The plasma channel 77 has a doughnut shape, which includes a downward open outlet port 77a (top part of FIG. 3). The outlet port 77a communicates with a process chamber (not shown) of a plasma etcher or a sputtering system with the plasma accelerating apparatus 60. An upper circle loop inductor 79 is disposed at an end wall 81 of the plasma channel 77. The upper circle loop inductor 79 applies RF energy to the gas in the plasma channel 77 to generate electrons. The generated electrons collide with neutral atoms of the gas to form a plasma beam. Internal and external circle loop inductors 71 and 73 in which coils are wound are disposed at an inner wall 82 and an outer wall 83 of the plasma channel 77, respectively. The internal and external circle loop inductors 71 and 73 are coaxially arranged in a line.
The operation of the plasma accelerating apparatus 60 will now be described with reference to FIG. 4. When a gas is supplied to an inside of the plasma channel 77 from a gas source (not shown), the upper circle loop inductor 79 applies RF energy to the supplied gas to generate electrons. Consequently, the electrons collide with neutral atoms of the gas, and the gas is ionized to produce a plasma beam.
The internal and external circle loop inductors 71 and 73 induce a magnetic field B and a secondary electric current J in the plasma channel 77 to form an electromagnetic force F, which accelerates the plasma beam toward an outlet port 77a of the plasma channel 77.
Since such a plasma accelerating apparatus 60 accelerates ions in the same direction regardless of a polarity of the electromagnetic force F, an anode electrode and a cathode electrode that conventional electrostatic type accelerating apparatuses 10 and 40 require become unnecessary. This leads to a simple construction thereof. Furthermore, the plasma accelerating apparatus 60 adjusts an electric current through the internal and external circle loop inductors 71 and 73. By using the inductors, the generated electromagnetic force F may be more easily adjusted.
However, in the plasma etcher or the sputtering system using the plasma accelerating apparatus 60, an etching rate for an etching or sputtering generation process depends on ion energy and plasma density. Further, plasma density is influenced by RF energy applied to the plasma channel 77, an electromagnetic force F formed by an electric field B and a secondary current J induced inside the plasma channel 77, and an amount of a secondary electron generated in first, second, and third walls 81, 82, and 83 of the plasma channel 77.
That is, in a condition having the same dielectric constant, when a secondary electron emission coefficient is great, the plasma density is increased. A relation between the plasma density and the secondary electron emission coefficient is disclosed in an article of J.J.A.P. Vol 38, 1999, Part 1, No. 9A, p. 5247. Accordingly, the secondary electron emission coefficient becomes an important variable to determine a performance of a plasma etcher or a sputtering system. However, conventionally, the plasma channel 77 has been made of SiO2 such as quartz or a non-conductive material such as Pyrex. Such a material has a disadvantage in that an electron amplification rate is low thus elevating an acceleration voltage because a secondary electron emission coefficient is not a sufficiently high.
In order to address these and other problems, a plasma accelerating apparatus having a MgO coating layer formed on an inner surface of the plasma channel as a secondary electron emission layer emitting a secondary electron has been proposed and used. In the conventional plasma accelerating apparatus, there is a limitation to obtain sufficient secondary electron emission effect in a discharge space of the plasma channel by only a coating layer of a signal material having MgO. Therefore, what is needed is a plasma accelerating apparatus capable of obtaining a sufficient secondary electron emission effect in a discharge space of a plasma channel to optimize a performance of a plasma etcher or a sputtering system.